[[Image: Ancestors of Dolphins.jpg|thumb|300px|right|Dolphins evolved from terrestrial animals into aquatic animals throughout generations of evolution. The dolphins share numerous ancestors with the bowhead whale. https://sites.google.com/site/obenscience7e/unit-1-why-do-organisms-look-like-that/a-case-study-how-modern-whales-came-to-be.]]

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[[Image: AncestorsofDolphins.jpg|thumb|300px|right|Dolphins evolved from terrestrial animals into aquatic animals throughout generations of evolution. The dolphins share numerous ancestors with the bowhead whale. https://sites.google.com/site/obenscience7e/unit-1-why-do-organisms-look-like-that/a-case-study-how-modern-whales-came-to-be.]]

The evolution of dolphins, or <i>Delphinus</i>, is believed to have started with the <i>Pakiectus</i> a four legged, land walking mammal. The <i>Pakiectus</i> dates back to approximately 50 million years ago. Throughout the centuries, these animals have gone through drastic changes to become the modern day dolphin. Along with the <i>Pakiectus</i>, the dolphin is thought to have evolved alongside or from the <i>Ambulocetus</i>, <i>Protocetid</i>, <i>Dorudontid</i>, <i>Squalodontidae</i>, <i>Aetiocetidae</i>, and <i>Kentriodontidae</i> to eventually become the <i>Delphinus</i>.<ref>[https://dolphin-academy.com/learn/evolution]</ref> The Pakiectus lived near the shallow waters and began to feed on organisms that lived in these waters, which began the transition from terrestrial to aquatic animals. The bone structure of the flipper in the modern dolphin is very similar to the structure found in the Pakiectus legs and hooves, confirming the link between the two organisms.<ref>[https://www.dolphins-world.com/dolphin-evolution/]</ref>

The evolution of dolphins, or <i>Delphinus</i>, is believed to have started with the <i>Pakiectus</i> a four legged, land walking mammal. The <i>Pakiectus</i> dates back to approximately 50 million years ago. Throughout the centuries, these animals have gone through drastic changes to become the modern day dolphin. Along with the <i>Pakiectus</i>, the dolphin is thought to have evolved alongside or from the <i>Ambulocetus</i>, <i>Protocetid</i>, <i>Dorudontid</i>, <i>Squalodontidae</i>, <i>Aetiocetidae</i>, and <i>Kentriodontidae</i> to eventually become the <i>Delphinus</i>.<ref>[https://dolphin-academy.com/learn/evolution]</ref> The Pakiectus lived near the shallow waters and began to feed on organisms that lived in these waters, which began the transition from terrestrial to aquatic animals. The bone structure of the flipper in the modern dolphin is very similar to the structure found in the Pakiectus legs and hooves, confirming the link between the two organisms.<ref>[https://www.dolphins-world.com/dolphin-evolution/]</ref>

The evolution of dolphins, or Delphinus, is believed to have started with the Pakiectus a four legged, land walking mammal. The Pakiectus dates back to approximately 50 million years ago. Throughout the centuries, these animals have gone through drastic changes to become the modern day dolphin. Along with the Pakiectus, the dolphin is thought to have evolved alongside or from the Ambulocetus, Protocetid, Dorudontid, Squalodontidae, Aetiocetidae, and Kentriodontidae to eventually become the Delphinus.[1] The Pakiectus lived near the shallow waters and began to feed on organisms that lived in these waters, which began the transition from terrestrial to aquatic animals. The bone structure of the flipper in the modern dolphin is very similar to the structure found in the Pakiectus legs and hooves, confirming the link between the two organisms.[2]

Over the 50 million years of evolution, the ancestors of dolphins adapted from being terrestrial to aquatic. A characteristic that is mainly found in terrestrial animals is that of a vertical spine. Dolphins have vertical spines leaving them swimming with vertical movements, while fish movements are horizontal.[3] In comparison to the Pakiectus, dolphins hav much larger skulls with a shape that has adapted to accommodate for a padded lower jaw and extended middle ear. Having an extended middle ear allows the dolphins to use echolocation for communication. As the ancestors of dolphins moved toward living aquatically, the nostrils evolved into a blowhole to expend less energy while surfacing to breathe. The ancestors of dolphins that lived terrestrially had legs to walk. Dolphins have two small pelvic bones that are rod shaped that are now vestigial legs from their land walking ancestors.[4]